Seeinstructions): Project 2. Enhancing Glioma Immunotherapy with Temodar-lnduced Lymphopenia and a Multivalent Vaccine. John H. Sampson, M.D., Ph.D., M.H.Sc., Project Leader Despite the demonstrated capacity for the immune system to eliminate tumor cells with exquisite precision in preclinical models, active immunotherapy against human neoplasms has met with relatively few clinical successes. However, our vaccines targeting the tumor-specific epidermal growth factor receptor mutation, EGFRvlll, when given during recovery from temozolomide (TMZ)-induced lymphopenia have produced strong humoral and CD8+ and CD4+ T-cell responses that are accompanied by radiographic responses in all patients with residual disease and a median survival that exceeds 32 months. Vaccination eliminates EGFRvlll-expressing tumor cells. This illustrates the effectiveness of immunologic targeting, but EGFRvlll-negative tumor recurrence in this setting underscores the need to develop an effective therapy that addresses the heterogeneity of antigen expression in GBM. We believe that the potent and specific immune responses generated against EGFRvlll in our studies were potentiated by TMZ. The homeostatic proliferation that occurs after TMZ-induced lymphodepletion reduces the threshold for lymphocyte activation and proliferation. Our murine models have demonstrated that vaccine responses can be dramatically enhanced in TMZ-pretreated mice in a dose-dependent manner and dose-intensified TMZ regimens in patients with GBM have resulted in dramatically enhanced cellular and humoral responses to vaccination. These results have highlighted the potential to leverage the recovery from TMZ-induced lymphopenia as a potentially novel mechanism to enhance active immunotherapy against GBM. In an attempt to broaden the response seen when targeting EGFRvlll in this context, we propose to evaluate total tumor-RNA loaded dendritic cell vaccines. Mechanistic understanding of the effects of TMZ on the induction and maintenance of antitumor immunity will be explored in relevant murine astrocytoma models in order to rationally develop enhanced immunotherapeutic treatments for patients with GBM. RELEVANCE (See instructions): Treatment for malignant primary brain tumors is ineffective and represents the most expensive medical therapy per quality-adjusted life-year saved currently provided in the USA. The only major side effect of temozolomide, the only successful chemotherapeutic for this disease, is bone marrow suppression. We believe this suppression may dramatically enhance antitumor immunity and will investigate this possibility.